The present invention relates to a magnetic recording head having a function for inducing magnetization reversal by applying a high-frequency magnetic field to a magnetic recording medium, and to a magnetic recording and reproduction device.
In order to achieve higher recording densities for a magnetic recording head mounted in a hard disk device, it is necessary to narrow the width and pitch of write tracks, and thus correspondingly narrow the magnetically recorded bits encoded in each write track. One challenge in narrowing the width and pitch of write tracks is decreasing a surface area of a main pole of the magnetic recording head at an air bearing surface of the recording media. Specifically, as the main pole becomes smaller, the recording field becomes smaller as well, limiting the effectiveness of the magnetic recording head, and at some degree of miniaturization, with prior technology it is no longer possible to achieve a recording field sufficient to effectively record magnetic information into the media with such a conventional recording head. One prior technology that has been proposed to address this issue is a high-frequency magnetic field-assisted recording method (MAMR: microwave-assisted magnetic recording), in which a spin torque oscillator (STO) is formed on the main pole, and a high-frequency magnetic field is applied to the recording medium in order to reduce the coercive force of the medium, and in this state, a recording field is applied to the medium in order to record data. Heusler alloys have been incorporated into the field generating layer (FGL) and spin polarized layer (SPL) of the STO, thereby achieving high spin polarization (P) and relatively low saturation magnetic flux density (Bs) which are associated with high spin torque efficiency.
One challenge with spin torque oscillators is that it is difficult to manufacture them to have a high spin torque efficiency. One factor that can negatively affect spin torque efficiency is defects in the crystal structure of the Heusler alloy in the spin polarized layer (SPL) and/or field generating layer (FGL) of the STO, especially when crystallizing the Heusler alloy in a Heusler layer above an interlayer with fcc structure. Conventional MAMR heads have addressed this problem by configuring a thick enough interface CoFe layer with bcc structure between the interlayer and the Heusler alloy in the Heusler layer. Although the thick interface CoFe layer promotes proper crystalline growth for the Heusler layer, the high magnetic flux density of the interface CoFe layer also compromises spin torque efficiency. When the interface CoFe layer is thin, the initial part of the Heusler layer creates a magnetic dead layer within the Heusler alloy that also contributes to lowered spin torque efficiency by reducing the functional thickness of the Heusler layer.